Carbon has been used by mankind since the discovery of fire. Charcoal is a blackish residue consisting of impure carbon obtained by removing water and other volatile constituents from plastics, tires, rubber, animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood, sugar, bone char, or other substances in an oxygen deprived atmosphere. The resulting carbon ranges in hardness and can be brittle, lightweight, black, porous material, which resembles coal. Charcoal produced in this manner is 65% to 98% carbon with the remainder consisting of volatile chemicals and ash.
Charcoal may be activated to produce activated carbon, which has an increased effectiveness as a filter. Activated carbon readily absorbs a wide range of organic compounds dissolved or suspended in gases and liquids. Charcoal or activated carbon is often used to filter water to remove bacteria and undesired tastes. In certain industrial process, such as the purification of sucrose from cane sugar, impurities cause an undesirable color, which can be removed with activated, carbon. Activated carbon is also used to absorb odors and toxins in gases, such as mercury. Charcoal or activated carbon filters are also used in some types of gas masks. In medical uses, activated carbon is mainly exploited for its capacity to absorb poisons. In addition, activated carbon can be used to reduce discomfort and embarrassment due to excess gas in the digestive tract. Charcoal is often classified by its properties and the grade of porosity of activated carbon can depend on the properties of the charcoal starting material and method of activation.
The production of activated carbon begins with the production of charcoal. Making charcoal is a lengthy process wherein biomass is typically slowly smoldered in a pile over several days. The charcoal is then cooled in an inert atmosphere. Activated carbon is then produced by removing hydrocarbons and materials from the opening structure of the charcoal with steaming, chemical treatment or a combination thereof. These steps are time consuming and expensive.
During the process of making charcoal, a synthetic gas, which can be a mixture including carbon dioxide, nitrogen, methane, carbon monoxide and hydrogen is produced as a waste product. During the late 1800's synthetic gas was used in Europe to provide heating and power generation using charcoal and peat as a feed material. During World War II, the shortage of petroleum lead to a renewed interest in synthetic gas. It was estimated that over 500,000 vehicles were running on such gas. This gas can be burned as a fuel or converted to a petroleum substitute by means of a Fischer-Tropsch process. That process features a catalyzed chemical reaction in which synthesis gas is converted into liquid hydrocarbons of various forms. Often, catalysts based on iron and cobalt are utilized in the process, although nickel and ruthenium have also been used. The principal purpose of this process is to produce a synthetic petroleum substitute for use as synthetic lubrication oil or as synthetic fuel. This synthetic fuel can be used to run trucks, cars and some aircraft engines. The use of diesel is increasing in recent years.
A Fischer-Tropsch process involves a variety of chemical reactions, which lead to a series of products. The reactions include those resulting in the formation of alkanes. These can be described by chemical equations of the form:(2n+1)H2+nCO→CnH(2n+2)+nH2Owhere n is a positive integer. The simplest of these (n=1), results in formation of methane. Process conditions and catalyst composition can be chosen to favor higher order reactions where (wherein n>1). Alkanes produced in this manner can be straight-chained and branched alkanes. In addition to alkane formation, other reactions result in the formation of alkenes, as well as alcohols and other oxygenated hydrocarbons. Another reaction in a Fischer-Tropsch process is the water gas shift reaction:H2O+CO→H2+COThis reaction results in formation of CO2, which can be used to shift the H2:CO2 ratio of incoming synthesis gas.
The process also allows for the use of catalyst to produce the Sabatier reaction. This can be used to elevate the production of methane, which allows for the gas to be used in a wider variety of internal combustion engines. The Sabatier reaction, which was discovered by the French chemist Paul Sabatier, involves passing the synthetic gas over a catalyst to produce methane and water as follows:CO2+4H2→CH4+2H2O